Light wavelength conversion member and light-emitting device

ABSTRACT

In one aspect of the present disclosure, there is provided an optical wavelength conversion member including a polycrystalline ceramic sintered body containing, as main components, Al 2 O 3  crystal grains and crystal grains represented by formula X 3 Al 5 O 12 :Ce. In the optical wavelength conversion member  9 , atoms of element X are present also in an Al 2 O 3  crystal grain adjacent to the interface between the Al 2 O 3  crystal grain and an X 3 Al 5 O 12 :Ce crystal grain.

CROSS-REFERENCE TO RELATED APPLICATIONS

This international application claims priority to Japanese PatentApplication No. 2018-143791 filed in the Japan Patent Office on Jul. 31,2018, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an optical wavelength conversionmember and a light-emitting device, each of which can convert lightwavelength and is used for, for example, wavelength conversionapparatuses, fluorescent materials, lighting apparatuses, and videoapparatuses.

BACKGROUND ART

A head lamp, a projector, a lighting apparatus, or a similar apparatusgenerally includes a device for achieving white light through wavelengthconversion, by means of a fluorescent body (i.e., a wavelengthconversion member), of blue light emitted from a light-emitting diode(LED) or a laser diode (LD).

Hitherto, the matrix or material of the fluorescent body (or a phosphor)has been, for example, a resin material or a glass material. Inaccordance with a trend for using a high-output light source in recentyears, the phosphor is required to have higher durability. Thus, ceramicphosphors have received attention.

Known ceramic phosphors are formed of a Ce-activated garnet (A₃B₅O₁₂)component, such as Y₃Al₅O₁₂:Ce (YAG:Ce).

For example, Patent Documents 1 and 2 disclose a technique for formingan Al₂O₃—YAG:Ce composite material exhibiting improved heat resistanceand thermal conductivity.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Application Laid-Open (kokai) No.    2014-132084-   Patent Document 2: International Publication WO 2004/065324

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

According to the techniques disclosed in Patent Documents 1 and 2, anAl₂O₃-YAG:Ce composite material is formed from Al₂O₃ particles andYAG:Ce particles during production of a phosphor. However, thetechniques may cause the problems described below due to a largedifference in lattice constant between Al₂O₃ and YAG.

When adjacent crystal grains exhibit a lattice mismatch (i.e., a largedifference in lattice constant) at the interface between the crystalgrains (i.e., grain boundary), a defect (e.g., dislocation) may occur atthe interface.

When such a defect occurs, the defect becomes a non-luminescentrecombination center (i.e., a site where energy is converted not intolight but into, for example, heat), which causes a reduction in internalquantum efficiency (i.e., emission efficiency). The term “internalquantum efficiency” as used herein refers to the ratio of the number ofgenerated photons to the number of injected and recombined electrons.

For example, the technique disclosed in Patent Document 1 involvespreparation of a phosphor using eutectic transformation of Al₂O₃ and YAG(each of which is in a single-crystal form). Thus, a large difference inlattice constant between Al₂O₃ and YAG may cause a reduction in internalquantum efficiency.

The technique disclosed in Patent Document 2 causes precipitation of aCeAl₁₁O₁₈ phase (i.e., a third component) during production of anAl₂O₃-YAG composite phosphor. The third component has a lattice constantsmaller than that of Al₂O₃. This causes a larger difference in latticeconstant, possibly resulting in a reduction in internal quantumefficiency.

Thus, according to the aforementioned conventional techniques, a largedifference in lattice constant between Al₂O₃ and YAG may cause a problemin terms of low emission efficiency (i.e., impairment of fluorescentcharacteristics) due to a reduction in internal quantum efficiency.

In one aspect of the present disclosure, there is preferably provided anoptical wavelength conversion member and a light-emitting device, each,of which exhibits high internal quantum efficiency and superiorfluorescent characteristics.

Means for Solving the Problem

(1) One aspect of the present disclosure is directed to an opticalwavelength conversion member comprising a polycrystalline ceramicsintered body containing, as main components, Al₂O₃ crystal grains andcrystal grains represented by formula X₃Al₅O₁₂:Ce.

In the optical wavelength conversion member, X of X₃Al₅O₁₂:Ce is atleast one element selected from the following element group:

X: lanthanoids (except for Ce), Y, and Sc; and

atoms of element X are present also in an Al₂O₃ crystal grain adjacentto the interface between, the Al₂O₃ crystal grain and an X₃Al₅O₁₂:Cecrystal grain.

In the optical wavelength conversion, member, as described above, atomsof element X are present also in an Al₂O₃ crystal grain adjacent to theinterface between, the Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystalgrain (i.e., atoms of element X are incorporated into the Al₂O₃ crystalgrain through atomic, substitution). Thus, the optical wavelengthconversion member exhibits high internal quantum efficiency and superiorfluorescent characteristics (i.e., high emission intensity).

More specifically, since the optical wavelength conversion member hasthe aforementioned structure, lattice mismatch is mitigated at theinterface between an Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystalgrain. Thus, defects are reduced at the interface, and the influence ofa non-luminescent recombination center is suppressed, resulting inimproved internal quantum efficiency (i.e., improved emissionefficiency).

Consequently, fluorescent characteristics (specifically, emissionintensity) are improved. Also, temperature rise can be prevented, sinceinternal quantum efficiency is improved, and energy can be convertedefficiently into light without conversion to heat. Therefore,temperature quenching (i.e., thermal quenching) can be reduced, thusimproving heat resistance.

In the optical wavelength conversion, member, the ceramic sintered bodyhas a garnet structure represented by X₃B₅O₁₂:Ce (wherein B is Al),wherein X is at least one element selected from the aforementionedelement group. This structure enables efficient conversion of blue lightinto visible light.

(2) In the optical wavelength conversion member, atoms of element X maybe present at depths of 1 nm to 20 nm as measured from the surface ofthe Al₂O₃ crystal, grain adjacent to the interface.

When atoms of element X are present (through atomic substitution) atdepths of 1 nm or more as measured from the surface of the Al₂O₃ crystalgrain, lattice mismatch at the interface can be further mitigated. Thus,defects are further reduced at the interface (grain boundary), and theinfluence of a non-luminescent recombination center is greatlysuppressed, leading to a considerable improvement in internal quantumefficiency (i.e., emission efficiency). Since temperature quenching canalso be further reduced, heat resistance is greatly improved.

Meanwhile, when atoms of element X are present (through atomicsubstitution) at depths greater than 20 nm as measured from the surfaceof the Al₂O₃ crystal grain, the effect of mitigating lattice mismatch issuppressed at the interface between, the Al₂O₃ crystal grain and theX₃Al₅O₁₂:Ce crystal grain, resulting in less improvement in theaforementioned characteristics.

Therefore, preferably, atoms of element X are present in theaforementioned region (i.e., at depths of 1 nm to 20 nm as measured fromthe surface of the Al₂O₃ crystal grain).

In the case of determination of a region where atoms of element X arepresent, measurement can be performed at a plurality of (e.g., five ormore) positions in one Al₂O₃ crystal grain, and the measurement can beperformed in a plurality of (e.g., five or more) Al₂O₃ crystal grains,followed by calculation of the average of the resultant measurements.

(3) The aforementioned optical wavelength conversion, member comprisesthe aforementioned optical wavelength conversion member and alight-emitting element.

The light (i.e., fluorescence) having a wavelength converted by means ofthe light-emitting device (specifically, the optical wavelengthconversion member) exhibits high emission intensity. The opticalwavelength conversion member exhibits high heat resistance.

The light-emitting element of the light-emitting device may be any knownelement, such as an LED or LD,

Characteristic Features of the Present Disclosure Will Now be Described>

The term “main component” refers to any component present in apredominant amount (i.e., volume) in the optical wavelength conversionmember. For example, the optical wavelength conversion member maycontain Al₂O₃ crystal grains as translucent grains and crystal grainsrepresented by formula X₃Al₅O₁₂:Ce (i.e., X₃Al₅O₁₂:Ce crystal grains) asfluorescent grains in a total amount of 50 vol. % or more (preferably 90vol. % or more).

The formula “X₃Al₅O₁₂:Ce” refers to a compound in which a portion ofelement X contained in X₃Al₅O₁₂ is substituted by Ce through formationof a solid solution. The compound having such a structure exhibitsfluorescent characteristics.

In X₃Al₅O₁₂:Ce crystal grains, Y may be essential as element X.

Examples of the lanthanoid (except for Ce) include La, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Trn, Yb, and Lu.

When the total amount of Al₂O₃ crystal grains and X₃Al₅O₁₂:Ce crystalgrains is 100 vol. %, the amount of X₃Al₅O₁₂:Ce crystal grains may be,for example, 3 vol. % to 70 vol. %.

Whether or not element X is contained in an Al₂O₃ crystal grain adjacentto the interface between the Al₂O₃ crystal grain and an X₃Al₅O₁₂:Cecrystal grain (i.e., the presence of X in the Al₂O₃ crystal grain) canbe detected in, for example, a region extending inward from the surfaceof the Al₂O₃ crystal grain, by a distance of 25 nm or less through, forexample, HAADF-STEM (high-angle annular dark-field scanning transmissionelectron microscopy).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Cross-sectional view (in a thickness direction) of alight-emitting device.

FIG. 2 Flow chart showing a production process for an optical wavelengthconversion member of an embodiment.

FIG. 3 Explanatory view showing a portion of an HAADF-STEM image of anoptical wavelength conversion member of Example 1.

DESCRIPTION OF REFERENCE NUMERALS

-   1: light-emitting device-   5: light-emitting element-   9: optical wavelength conversion member

MODES FOR CARRYING OUT THE INVENTION

Next will be described embodiments of the optical wavelength conversionmember and light-emitting device of the present disclosure.

1. Embodiment [1-1. Light-Emitting Device]

Now will be described a light-emitting device including an opticalwavelength conversion member according to the present embodiment.

As illustrated in FIG. 1, a light-emitting device 1 of the presentembodiment includes a box-shaped ceramic package (container) 3 formedof, for example, alumina; a light-emitting element 5 (e.g., LD) disposedin the interior of the container 3; and a plate-like optical wavelengthconversion member 9 disposed so as to cover an opening 7 of thecontainer 3.

In the light-emitting device 1, light emitted from the light-emittingelement 5 transmits through the translucent optical wavelengthconversion member 9, and the wavelength of a portion of the emittedlight is converted in the interior of the optical wavelength conversionmember 9. Thus, the optical wavelength conversion member 9 emitsfluorescence having a wavelength different from that of the lightemitted from, the light-emitting element 5.

For example, the optical wavelength conversion member 9 converts thewavelength of blue light emitted from an LD, whereby the opticalwavelength conversion member 9 as a whole emits white light to theoutside (e.g., upward in FIG. 1).

[1-2. Optical Wavelength Conversion Member]

The optical wavelength conversion member 9 will next be described.

The optical wavelength conversion member 9 of the present embodiment iscomposed of a polycrystalline ceramic sintered body containing, as maincomponents, Al₂O₃ crystal grains (i.e., translucent grains) and crystalgrains represented by formula X₃Al₅O₁₂:Ce (i.e., X₃Al₅O₁₂:Ce crystalgrains: fluorescent grains).

In the optical wavelength conversion, member 9, X of X₃Al₅O₁₂:Ce is atleast one element selected from the following element group. That is,the ceramic sintered body has a so-called garnet structure.

X: lanthanoids (except for Ce), Y, and Sc.

In the optical wavelength conversion member 9, atoms of element X arepresent also in an Al₂O₃ crystal grain adjacent to the interface betweenthe Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystal grain.

Furthermore, atoms of element X (e.g., atoms of Y) are present in aregion extending inward from the surface of the Al₂O₃ crystal grainadjacent to the aforementioned interface by a distance of, for example,25 nm or less. Preferably, atoms of element X (e.g., atoms of Y) arepresent at distances of 1 nm to 20 nm as measured from the surface ofthe Al₂O₃ crystal grain.

Notably, the formula X₃Al₅O₁₂:Ce corresponds to a combination ofelements (note: different elements) forming a substance represented bythe formula X₃Al₅O₁₂:Ce, wherein O is oxygen and Ce is cerium.

In the optical wavelength conversion member 9, the total amount of Al₂O₃crystal grains and X₃Al₅O₁₂:Ce crystal grains is, for example, 50 vol. %or more (preferably 90 vol. % or more, more preferably 100 vol. %); forexample, 99 vol. %.

When the total amount of Al₂O₃ crystal grains and X₃Al₅O₁₂:Ce crystalgrains is 100 vol. %, the amount of X₃Al₅O₁₂:Ce crystal grains is 3 vol.% to 70 vol. %; for example, 30 vol. %.

In the optical wavelength conversion member 9, the Ce concentration ofX₃Al₅O₁₂:Ce is 5 mol % or less (exclusive of 0) relative to element X.

[1-3. Production Method for Optical Wavelength Conversion Member]

A process for producing the optical wavelength conversion member 9 willnow be briefly and schematically described with reference to FIG. 2.

As detailed below in Experimental Examples, the optical wavelengthconversion member 9 is produced by means of reaction sintering.

As illustrated in FIG. 2, powder materials for the optical wavelengthconversion member 9 (i.e., ceramic sintered body) were weighed so as tosatisfy the aforementioned requirement of the embodiment (i.e., thepowder materials were prepared).

Subsequently, an organic solvent and a dispersant were added to theprepared powder materials, and these materials were ground and mixed ina ball mill.

Subsequently, the powder prepared through grind-mixing was mixed with aresin, to thereby prepare a slurry.

The slurry was then formed into a sheet compact through doctor blading.

The sheet compact was then debindered.

The debindered sheet compact was fired in a firing-atmosphere having apressure of 10⁴ Pa or more and an oxygen concentration of 0.8 vol. % to21 vol. % for a predetermined period of time. The ceramic sintered bodywas thereby produced.

[1-4. Effects]

The effects of the present embodiment will now be described.

(1) In the optical wavelength conversion member 9 of the presentembodiment, atoms of element X are present also in an Al₂O₃ crystalgrain adjacent to the interface (i.e., first crystal grain boundary)between the Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystal grain. Thus,the optical wavelength conversion member exhibits high internal quantumefficiency and superior fluorescent characteristics (i.e., high emissionintensity).

Specifically, since a portion of elements forming Al₂O₃ crystal grainsis substituted by atoms of element X during production of the opticalwavelength conversion member 9, lattice mismatch is mitigated at theinterface between an Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystalgrain. Thus, defects are reduced at the interface, and the influence ofa non-luminescent recombination center is suppressed, resulting inimproved, internal quantum efficiency (i.e., improved, emissionefficiency).

Consequently, fluorescent characteristics (specifically emissionintensity) are improved. Also, temperature rise can be prevented, sinceinternal quantum efficiency is improved, and energy can be efficientlyconverted into light without conversion to heat. Therefore, temperaturequenching can be reduced, and thus heat resistance is improved.

(2) In the present embodiment, atoms of element X are present at depthsof 1 nm to 20 nm as measured from the surface of the Al₂O₃ crystal grainadjacent to the aforementioned interface.

Therefore, lattice mismatch at the interface can be further mitigated.Thus, defects are further reduced at the interface (grain boundary), andthe influence of a non-luminescent recombination center is greatlysuppressed, leading to a considerable improvement in internal quantumefficiency (i.e., emission efficiency). Since temperature quenching canalso be further reduced, neat resistance is greatly improved.

(3) In the present embodiment, the ceramic sintered body has a garnetstructure represented by X₃Al₅O₁₂:Ce wherein X is at least, one elementselected from the aforementioned element group. This structure enablesefficient conversion of blue light into visible light.

(4) The light (i.e., fluorescence) having a wavelength converted bymeans of the light-emitting device 1 (specifically, the opticalwavelength conversion member 9) of the present embodiment exhibits highemission intensity and high color uniformity.

2. Experimental Examples

Next, will be described, for example, specific examples of theaforementioned embodiment.

Optical wavelength conversion member samples (Nos. 1 to 10) shown inTable 1 below were prepared.

Samples Nos. 1 to 6 and 8 to 10 fall within the scope of the presentdisclosure (Examples), and sample No. 7 falls outside the scope of thepresent disclosure (Comparative Example).

[2-1. Evaluation of Samples]

As described below, the samples were evaluated for the following items.

<Open Porosity>

The open porosity of the ceramic sintered body of the optical wavelengthconversion member of each sample was determined through the methodaccording to JIS R1634,

<Determination of Ions Present at Grain Boundary and Vicinity Thereof>

The ceramic sintered body of the optical wavelength conversion member ofeach sample was subjected to mechanical polishing, to thereby form, adisk (ϕ: 3 mm, thickness: t=50 to 100 μm). Subsequently, the center ofthe disk was subjected to dimpling, and then a through hole was providedin the center through ion milling, to thereby prepare a sample for STEM(scanning transmission electron microscopy).

As described below, STEM observation was performed at a thinnest portionaround the through hole (opening) of the above-prepared sample for STEM.

The observation was performed at a first crystal grain boundary (i.e.,the interface between an Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystalgrain) and at a second crystal grain boundary (i.e., the interfacebetween, two Al₂O₃ crystal grains).

Specifically, the orientation was adjusted so as to determine the atomicarrangement of Al of Al₂O₃ at the aforementioned first and secondcrystal grain boundaries while searching for a site where the atomicarrangement of the adjacent crystal grain was able to be observed, andthe atomic arrangement of Al of Al₂O₃ crystal grain was observed in anHAADF-STEM image having an atomic-number-dependent brightness, tothereby determine the presence or absence of atomic substitution, ofanother element (e.g., Y of element X) in the Al atomic arrangement.

The HAADF-STEM observation of the atomic arrangement was performed bymeans of a high-resolution STEM equipped with a Cs corrector. Thepresence or absence of an element (other than Al) at the second crystalgrain boundary was non-quantitatively determined by means of an EDS(energy dispersive X-ray spectrometer).

<Determination of Position of X Substitutions>

The sample used for the aforementioned determination of the presence ofions was used to determine a position where elemental Y (of element X)was present in an Al₂O₃ crystal grain adjacent to the interface betweenthe Al₂O₃ crystal grain and an X₃Al₅O₁₂:Ce crystal grain.

Specifically, line analysis was performed in the Al₂O₃ crystal grainadjacent to the aforementioned interface at a portion near the firstcrystal grain boundary, and determination of a region wherein elementalY (of element X) was present was started from a point (referenceinterface) at which the EDS detection value (i.e., output value) ofelemental Y was 50%. The line analysis was performed in a directionnormal to the interface.

The measurement was performed at any 20 points along a line whichextends across the interface between an Al₂O₃ crystal grain and anX₃Al₅O₁₂:Ce crystal grain in a direction normal to the interface. Thus,the average of detection values of elemental Y was determined.Subsequently, the measurement was performed in a plurality of (e.g.,five) Al₂O₃ crystal grains, and the average of average detection valuesof elemental Y in these grains was calculated, to thereby determine aregion of the presence of elemental Y.

<Internal Quantum Efficiency>

Optical wavelength conversion member samples (dimensions: 13 mm inwidth×13 mm in length×0.2 mm in thickness) were prepared.

The internal quantum efficiency of each sample was measured by means ofa fluorescence spectrophotometer manufactured by JASCO Corporation. BlueLD light (i.e., laser light) having a wavelength of 465 nm was used asan excitation light source.

The internal quantum efficiency of each sample was evaluated by a valuerelative to the internal quantum efficiency (taken as 100) in the casewhere a single-crystal body (i.e., a YAG:Ce single-crystal body) wasused. The internal quantum efficiency is preferably 97 or more, morepreferably of 100 or more.

<Laser Output Tolerance>

Optical wavelength conversion member samples (dimensions: 13 mm inwidth×13 mm in length×0.2 mm in thickness) were prepared.

Blue LD light having a wavelength of 465 nm was focused to a width of0.15 nm by means of a lens, and each sample was irradiated with thefocused light. Light transmitted through the sample was focused with alens, and the emission intensity was measured by means of a powersensor. The sample was irradiated with the blue LD light at a laserpower density of 0 to 50 W/nm².

Occurrence of temperature quenching was determined when the emissionintensity was reduced to 60% or less of that at a laser power density of5 W/nm².

A sample exhibiting no temperature quenching at 50 W/mm² was evaluatedas “Good” as shown in the column “LD output tolerance” of Table 2 below.A sample exhibiting no temperature quenching at 30 W/mm² or more andless than 50 W/mm² was evaluated as “Fair” as shown in the column “LDoutput tolerance” of Table 2. A sample exhibiting temperature quenchingat less than 30 W/mm² was evaluated as “Fail” as shown in the column “LDoutput tolerance” of Table 2. A sample exhibiting no temperaturequenching at 50 W/mm² or more is preferred in terms of laser outputtolerance.

<Emission Intensity>

Optical wavelength conversion member samples (dimensions: 13 mm inwidth×13 mm in length×0.2 mm in thickness) were prepared.

Blue LD light (i.e., laser light) having a wavelength of 465 nm wasfocused to a width of 0.15 mm by means of a lens, and each sample wasirradiated with the focused light. Light transmitted through the samplewas focused with a lens, and the emission intensity was measured bymeans of a powder sensor. The sample was irradiated with the light at alaser power density of 40 W/mm².

The emission intensity of each sample was evaluated by a value relativeto the emission intensity (taken as 100) in the case where asingle-crystal body (i.e., a YAG:Ce single-crystal body) was used. Theemission intensity is preferably 96 or more, more preferably 100 ormore.

[2-2. Sample Production Method and Evaluation Results]

Next will be described a production method for each sample and theresults of evaluation of the sample.

Example 1

Optical wavelength conversion members (samples Nos. 1 to 6) wereprepared, under the conditions shown in Table 1 below. Specifically,optical wavelength conversion members (samples Nos. 1 to 6) wereprepared through reaction sintering.

(1) Firstly, a ceramic sintered body (fluorescent body) was preparedthrough the procedure described below.

Specifically, as shown in Table 1, Al₂O₃ powder (mean particle size: 0.2μm), Gd₂O₃ powder (mean particle size: 0.9 μm), and CeO₂ powder (meanparticle size: 1.5 μm) were weighed so as to achieve the composition ofthe ceramic sintered body of each of samples Nos. 1 to 6.

The amount of X₃B₅O₁₂:Ce was maintained constant at 30 vol. % relativeto the entire ceramic sintered body. As shown in Table 1, X is Y and Gd,and B is Al. Thus, X₃B₅O₁₂:Ce is (Y,Gd)₃Al₅O₁₂:Ce.

These powder materials were added to a ball mill together with ethanol,and these materials were grind-mixed for 16 hours. The resultant slurrywas dried and formed into granules. A predetermined amount (2 wt. % oftotal) of a completely melted binder was added to the granules, and themixture was thoroughly stirred and dried, to thereby yield apredetermined powder.

The resultant powder was subjected to press molding and then CIPmolding, to thereby prepare a compact. The compact was debindered andthen fired in an air atmosphere, to thereby prepare a ceramic sinteredbody (i.e., optical wavelength conversion member). This firing wasperformed under the following conditions: a firing temperature of 1,600°C., a retention time of 10 hours, and a modified temperature loweringrate.

(2) The optical wavelength conversion member of each sample wasevaluated by the aforementioned evaluation methods. The results ofevaluation are shown in FIG. 3 and Table 2 below.

FIG. 3 shows an image obtained through HAADF-STEM observation. In FIG.3, a bright and whitish area (represented by YAG) corresponds to a(Y,Gd)₃Al₅O₁₂:Ce crystal grain, whereas a dark and blackish area(represented by Al₂O₃) corresponds an Al₂O₃ crystal grain.

As is clear from FIG. 3, bright points corresponding to atoms of anelement heavier than any of the elements forming Al₂O₃ are present in aportion of the Al₂O₃ crystal grain near the boundary (first crystalgrain boundary: interface) between the (Y,Gd)₃Al₅O₁₂:Ce crystal grainand the Al₂O₃ crystal grain; i.e., bright points are present in thevicinity of the surface of the Al₂O₃ crystal grain.

The EDS analysis indicated that the bright points correspond to Y. Thus,Y was found to be present in the Al₂O₃ crystal grain adjacent to thefirst crystal grain boundary. In Table 2, “Presence” in the column“Determination of Y by EDS” indicates that Y is present in the Al₂O₃crystal grain adjacent to the first crystal grain boundary.

Although not shown in Table 2, the presence of Gd was also confirmed inthe Al₂O₃ crystal grain adjacent to the first crystal grain boundary.

Y and Gd (which are element X) were found to be present in a regionextending inward from the surface of the Al₂O₃ crystal grain by adistance of 25 nm or less (i.e., a plurality of types of element X weredispersively present in this region). For example, element X was presentat a depth of 2 nm as measured from the surface of the Al₂O₃ crystalgrain.

Although not illustrated, the presence of Y was confirmed at the secondcrystal grain boundary (i.e., the interface between two Al₂O₃ crystalgrains), but not determined in the Al₂O₃ crystal grains.

Thus, samples Nos. 1 to 6 are produced by the method (i.e., reactionsintering) described in Table 2.

Therefore, the presence of Y in the Al₂O₃ crystal grain adjacent to thefirst crystal grain boundary is probably attributed to that Ysubstitution occurs in the crystal grain during reaction sintering.

Conceivably, an increase in temperature lowering rate causes an increasein the distance between the surface of the Al₂O₃ crystal grain adjacentto the first crystal grain boundary and an interior portion of thecrystal grain where atoms of Y are present through Y substitution.

As shown in Table 2, samples Nos. 1 to 6 are preferred in view that theyexhibit an internal quantum efficiency of 97 or more and a high emissionintensity of 96 or more because of the presence of Y in the Al₂O₃crystal grain adjacent to the first crystal grain boundary. Thesesamples are preferred in view that they exhibit an LD output toleranceof 30 w/mm² or more (evaluated as “Fair”) (i.e., low likelihood oftemperature quenching).

As shown in Table 2, samples Nos. 2 to 5 are particularly preferred inview that Y is present (through elemental substitution) at depths of 1nm to 20 nm as measured from the surface of the Al₂O₃ crystal grainadjacent to the first crystal grain boundary; hence they exhibit aninternal quantum efficiency of 104 or more and a high emission intensityof 123 or more. These samples are preferred in view that they exhibit anLD output tolerance of 50 W/nm² or more (evaluated as “Good”) (i.e., lowlikelihood of temperature quenching).

Samples Nos. 1 to 6 are preferred in view that they exhibit an openporosity of 0.02% and a high relative density of 99% or more.

Comparative Examples

An optical wavelength conversion member (sample No. 7) was preparedunder the conditions shown in Table 1 below.

The ceramic sintered body sample of Comparative Example 1 was preparedthrough a conventional mixing-system production method (see, forexample, Patent Document 1).

Specifically, raw materials were weighed so as to achieve a compositionof (Y,Gd)₃Al₅O₁₂:Ce (Gd: 15 mol % relative to Y). The raw materials wereadded to a ball mill together with ethanol, and these materials weregrind-mixed for 16 hours. The resultant slurry was dried and formed intogranules. The granules were formed into a compact, and the compact wasfired in an air atmosphere at 1, 600° C. for 10 hours, to thereby yielda sintered body. The sintered body was ground by means of an aluminamortar and then subjected to classification, to thereby prepare a powderhaving a mean particle size of 1 to 2 μm.

The resultant powder and alumina powder were mixed in predeterminedproportions so as to achieve a composition of sample No. 7. These powdermaterials were added to a ball mill together with ethanol, and thesematerials were grind-mixed for 16 hours. The resultant slurry was driedand formed into granules. The granules were formed into a compact, andthe compact was fired in an air atmosphere at 1,600° C. for 10 hours, tothereby yield a sintered body (i.e., sample No. 7 shown in Table 1).

Sample No. 7 was evaluated in the same manner as in Example 1. Theresults are shown in Table 2 below.

As is clear from Table 2, Y is not present in the Al₂O₃ crystal grainadjacent to the first crystal grain boundary in sample No. 7. Thus, thissample is not preferred in view that it exhibits an internal quantum,efficiency of 90, an emission intensity of 95, and an LD outputtolerance of 23 W/mm² (evaluated as “Fail”) (i.e., high likelihood oftemperature quenching).

Example 2

Optical wavelength conversion members (samples Nos. 8 to 10) wereprepared under the conditions shown in Table 1 below. Specifically,optical wavelength conversion members (samples Nos. 8 to 10) wereprepared, through reaction sintering.

Basically, each sample was prepared through the same procedure as inExample 1. However, materials used in Example 2 are slightly differentfrom those used in Example 1. The difference will now be described.

Specifically, Al₂O₃ powder (mean particle size: 0.2 μm), Y₂O₃ powder(mean particle size: 1.2 μm), and CeO₂ powder (mean particle size: 1.5μm) were weighed so as to achieve the composition of the ceramicsintered body of sample No. 8 shown, in Table 1, to thereby prepare apowder for sample No. 8.

Separately, Al₂O₃ powder (mean, particle size: 0.2 μm), Y₂O₃ powder(mean particle size: 1.2 μm), Lu₂O₃ powder (mean particle size: 0.9 μm),and CeO₂ powder (mean particle size: 1.5 μm) were weighed so as toachieve the composition of the ceramic sintered body of sample No. 9shown, in Table 1, to thereby prepare a powder for sample No. 9.

Separately, Al₂O₃ powder (mean particle size: 0.2 μm), Y₂O₃ powder (meanparticle size: 1.2 μm), Sc₂O₃ powder (mean particle size: 0.9 μm), andCeO₂ powder (mean particle size: 1.5 μm) were weighed so as to achievethe composition of the ceramic sintered body of sample No. 10 shown inTable 1, to thereby prepare a powder for sample No. 10.

In the same manner as in Example 1 above, samples Nos. 8 to 10 wereprepared from the powders for samples Nos. 8 to 10, and the samples wereevaluated. The results are shown in Table 2 below.

As is clear from Table 2, Y is present in the Al₂O₃ crystal grainadjacent to the first crystal grain boundary in samples Nos. 8 to 10.

Although not shown in Table 2, the presence of Lu (sample No. 9) or Sc(sample No. 10) was also confirmed in the Al₂O₃ crystal grain adjacentto the first crystal grain boundary.

Y, Lu, and Sc (which are element X) were found to be present in a regionextending inward from the surface of the Al₂O₃ crystal grain by adistance of 25 nm or less; i.e., a plurality of types of element X weredispersively present in this region. For example, element X was presentat a position inward from the surface of the Al₂O₃ crystal grain by adistance of 2 nm.

Samples Nos. 8 to 10 are preferred in view that they exhibit an internalquantum efficiency of 100 or more, a high emission intensity of 100 ormore, and an LD output tolerance of more than 50 W/mm² (i.e., lowlikelihood of temperature quenching).

Samples Nos. 8 to 10 are preferred in view that they exhibit an openporosity of 0.02% or less and a high relative density of 99% or more,

TABLE 1 Al₂O₃ X₃B₅O₁₂:Ce Non Y ion Ce Production content content Ionother than amount in X content No. Ex. method X B (vol %) (vol %) Y in X(mol %) (mol %) 1 Ex. 1 Reaction Y, Gd Al 70 30 Gd 15 0.3 2 sintering Y,Gd Al 70 30 Gd 15 0.3 3 Y, Gd Al 70 30 Gd 15 0.3 4 Y, Gd Al 70 30 Gd 150.3 5 Y, Gd Al 70 30 Gd 15 0.3 6 Y, Gd Al 70 30 15 0.3 7 Comp. Mixing Y,Gd Al 70 30 Gd 15 0.3 Ex. 1 system 8 Ex. 2 Reaction Y Al 70 30 Noaddition 0.3 9 sintering Y, Lu Al 70 30 Lu 15 0.3 10 Y, Sc Al 70 30 Sc15 0.3

TABLE 2 Firing Temperature Open Internal Production Firing time loweringrate porosity Presence of Y Position of quantum LD output Emission No.Ex. method temperature (hr) (° C./min) (%) by EDS Y substitutionefficiency tolerance intensity 1 Ex. 1 Reaction 1600 10 10 0.02 Presence0.5 98 Fair 118 2 sintering 1600 10 30 0.02 Presence 1 104 Good 124 31600 10 60 0.02 Presence 5 110 Good 130 4 1600 10 90 0.02 Presence 10108 Good 126 5 1600 10 100 0.02 Presence 20 106 Good 123 6 1600 10 2000.02 Presence 25 97 Fair 96 7 Comp. Mixing 1600 10 — 2 Absence — 90 Fail95 Ex. 1 system 8 Ex. 2 Reaction 1600 10 30 0.01 Presence 5 115 Good 1259 sintering 1600 10 30 0.01 Presence 5 112 Good 122 10 1600 10 30 0.02Presence 5 109 Good 118

3. Other Embodiments

Needless to say, the present disclosure is not limited to theaforementioned embodiments, but may be implemented in various otherforms without departing from the scope of the disclosure.

(1) For example, a sample was prepared through firing in air in theExamples described above. However, a sample having the same performanceas that of the Examples can be prepared through another firingtechnique, such, as hot press firing, vacuum firing, firing in areductive atmosphere, HIP, or any combination of these.

(2) The aforementioned optical wavelength conversion member orlight-emitting device can be used for various applications, includingfluorescent bodies, optical wavelength conversion apparatuses, headlamps, lighting apparatuses, and optical apparatuses (e.g., projectors).

(3) No particular limitation is imposed on the light-emitting elementused in the light-emitting device. The light-emitting element may be anyknown element, such as an LED or LD.

(4) In the aforementioned embodiments, the function of a singlecomponent may be shared by a plurality of components, or a singlecomponent may exert the functions of a plurality of components. Some ofthe components in the aforementioned embodiments may be omitted. Atleast some of the components in the aforementioned embodiments may be,for example, added to or replaced with components in another embodiment.Embodiments of the present disclosure encompass any form included intechnical ideas specified by the appended claims.

What is claimed is:
 1. An optical wavelength conversion membercomprising a polycrystalline ceramic sintered body containing, as maincomponents, Al₂O₃ crystal grains and crystal grains represented byformula X₃Al₅O₁₂:Ce, wherein X of X₃Al₅O₁₂:Ce is at least one elementselected from the following element group: X: lanthanoids (except forCe), Y, and Sc; and atoms of element X are present also in an Al₂O₃crystal grain adjacent to the interface between the Al₂O₃ crystal grainand an X₃Al₅O₁₂:Ce crystal grain.
 2. An optical wavelength conversionmember according to claim 1, wherein said atoms of element X are presentat depths of 1 nm to 20 nm as measured from the surface of the Al₂O₃crystal grain adjacent to the interface.
 3. A light-emitting devicecomprising an optical wavelength conversion member as recited in claim 2and a light-emitting element.
 4. A light-emitting device comprising anoptical wavelength conversion member as recited in claim 1 and alight-emitting element.